Fire Alarm SLC Wiring Requirements

[Steven Stupienski]

I'm trying to obtain a permit to install a new addressable fire alarm system. The code official would like me to present a process and method in which to measure what the manufacturer has stated in the SLC wiring requirements of the manual. (see below) He would also like to know what tool I'll be using and whether or not I'm qualified to use this tool. This is the first time I've ever had this question posed to me. I would appreciate any input.

"The Maximum total capacitance of all SLC wiring (both between conductors and from any conductor to ground) should not exceed 0.5
micro farads"

 

[GoldDigger]

There are two ways to approach this. One is to try to get capacitance per foot to an adjacent grounded plate data from the wire manufacturer and add all the connected wires up. Not terribly promising and also unlikely to satisfy this inspector.
The other is to use either a specifically designed capacitance meter or a general purpose impedance bridge. Both measure the capacitance by imposing a (typically audio frequency) known AC voltage so that capacitance (or capacitance and inductance). If you know that you will only see capacitance, a meter can use a single frequency and measure the current.
These meters are generally easy to use as long as you have first determined that there are no shunt resistances or applied voltages present when you make the measurement.
If you are capable of reading and understanding the manufacturer's instructions you should be qualified to use it. Trying to get some sort of certification as proof of qualification is more of a problem. Possibly the equipment manufacturer offers courses?

 

[Steven Stupienski]

Thanks for this information. I'll be measuring existing 18 gauge thermostat cable that is in this two story, eight apartment unit facility. I have no idea of the distance, nor is the manufacturer of the cable easily seen. Would I expect to read picofarads assuming I disconnect all devices and create splices all the way through the circuit? Likely eight splices in the circuit. Any recommendation on electronic meters for this type of measurement?

 

[gadfly56]

Thanks for this information. I'll be measuring existing 18 gauge thermostat cable that is in this two story, eight apartment unit facility. I have no idea of the distance, nor is the manufacturer of the cable easily seen. Would I expect to read picofarads assuming I disconnect all devices and create splices all the way through the circuit? Likely eight splices in the circuit. Any recommendation on electronic meters for this type of measurement?

The highlighted above is a bit concerning. Is this a retrofit using existing cabling?

 

[Steven Stupienski]

This is a retrofit that is understood and approved by the local FM and the code official who's asking for the information regarding the maximum total capacitance of the wire as described in the manual of the fire alarm system manufacturer. Installing new cable would only be a last resort as it would require cutting up hard ceilings in all apartments or running wire mold. Officials are willing to bend on this as long as the manufacturers requirements are met. Shielded and twisted cable are not required for this system and 18 gauge wire is standard for this system, otherwise this would be a mute point. Interestingly enough, the Official would require the same capacitance information if new wire were installed since the system manual does not differentiate on new or existing wire.

Thanks for your help.

 

[gadfly56]

This is a retrofit that is understood and approved by the local FM and the code official who's asking for the information regarding the maximum total capacitance of the wire as described in the manual of the fire alarm system manufacturer. Installing new cable would only be a last resort as it would require cutting up hard ceilings in all apartments or running wire mold. Officials are willing to bend on this as long as the manufacturers requirements are met. Shielded and twisted cable are not required for this system and 18 gauge wire is standard for this system, otherwise this would be a mute point. Interestingly enough, the Official would require the same capacitance information if new wire were installed since the system manual does not differentiate on new or existing wire.

Thanks for your help.

OK, I guess GoldDigger's is the best suggestion. It's pretty easy to get a meter that will measure capacitance these days.